Question

Distance b/w object and its real image in convex lens is D and magnification in m find the focal length of lens?

Answer 1

Answer:

f = d/(2-m-1/m)

In order for this formula to work, two things have to be taken care of:

The distance is taken from image to object, so image position minus object position (d = img-obj).

The magnification m is negative for inverted images (the usual case with convex lenses: projection, real inverted image)

Explanation: